Oathstone

When Oathstone enters the battlefield, discard any number
of cards. Put an obligation counter on Oathstone for each card discarded in this way.
{t}, Remove an obligation counter from Oathstone: Choose one —
•Target player sacrifices a creature.
•Target player discards a card.
"I don't want to decide anymore. Before this Oathstone, before the spren, before my father, I promise to
do whatever this stone's holder demands of me. I am Truthless."
—Szeth-son-son-Vallano